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            <article id="post-遗传算法的基本概念和Java实现"
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        <time class="post-time" title="2017-08-28 09:24:57" datetime="2017-08-28T01:24:57.000Z"  itemprop="datePublished">2017-08-28</time>

        
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    <h3 class="post-title" itemprop="name">
      <a class="post-title-link" href="/2017/08/28/遗传算法的基本概念和Java实现/">遗传算法的基本概念和Java实现</a>
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        <blockquote>
<p>本文来自 Itimetraveler’s Blog： <a href="https://itimetraveler.github.io/2017/07/11/%E9%81%97%E4%BC%A0%E7%AE%97%E6%B3%95%E7%9A%84%E5%9F%BA%E6%9C%AC%E6%A6%82%E5%BF%B5%E5%92%8CJava%E5%AE%9E%E7%8E%B0/" target="_blank" rel="noopener">遗传算法的基本概念和Java实现</a></p>
</blockquote>
<p>基因遗传算法是一种灵感源于达尔文自然进化理论的启发式搜索算法。该算法反映了自然选择的过程，即最适者被选定繁殖，并产生下一代。本文简要地介绍了遗传算法的基本概念和实现，希望能为读者展示启发式搜索的魅力。</p>
<p>[<figure class="image-bubble">
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                    <div class="overlay"></div>
                    <img src="https://itimetraveler.github.io/gallery/genetic-algorithms/1-BYDJpa6M2rzWNSurvspf8Q.png" alt="如上图（左）所示，遗传算法的个体由多条染色体组成，每条染色体由多个基因组成。上图（右）展示了染色体分割和组合的方式。](https://itimetraveler.github.io/gallery/genetic-algorithms/1-BYDJpa6M2rzWNSurvspf8Q.png)" title>
                </div>
                <div class="image-caption">如上图（左）所示，遗传算法的个体由多条染色体组成，每条染色体由多个基因组成。上图（右）展示了染色体分割和组合的方式。](https://itimetraveler.github.io/gallery/genetic-algorithms/1-BYDJpa6M2rzWNSurvspf8Q.png)</div>
            </figure></p>
    

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        <time class="post-time" title="2017-08-27 15:52:21" datetime="2017-08-27T07:52:21.000Z"  itemprop="datePublished">2017-08-27</time>

        
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      <a class="post-title-link" href="/2017/08/27/bitmap/">【算法】10亿int型数，统计只出现一次的数</a>
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        <blockquote>
<p>本文来自 Itimetraveler’s Blog： <a href="https://itimetraveler.github.io/2017/07/13/%E3%80%90%E7%AE%97%E6%B3%95%E3%80%9110%E4%BA%BFint%E5%9E%8B%E6%95%B0%EF%BC%8C%E7%BB%9F%E8%AE%A1%E5%8F%AA%E5%87%BA%E7%8E%B0%E4%B8%80%E6%AC%A1%E7%9A%84%E6%95%B0/" target="_blank" rel="noopener">【算法】10亿int型数，统计只出现一次的数</a></p>
</blockquote>
<h2 id="题目"><a href="#题目" class="headerlink" title="题目"></a><strong>题目</strong></h2><p>10亿int整型数，以及一台可用内存为1GB的机器，时间复杂度要求O(n)，统计只出现一次的数？</p>
<h2 id="分析"><a href="#分析" class="headerlink" title="分析"></a>分析</h2><p>首先分析多大的内存能够表示10亿的数呢？一个int型占4字节，10亿就是40亿字节（很明显就是4GB），也就是如果完全读入内存需要占用4GB，而题目只给1GB内存，显然不可能将所有数据读入内存。</p>
<p>我们先不考虑时间复杂度，仅考虑解决问题。那么接下来的思路一般有两种。</p>
<ol>
<li><p><strong>位图法</strong>：用一个bit位来标识一个int整数。</p>
</li>
<li><p><strong>分治法</strong>：分批处理这10亿的数。</p></li></ol>
    

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        <time class="post-time" title="2017-08-27 11:50:13" datetime="2017-08-27T03:50:13.000Z"  itemprop="datePublished">2017-08-27</time>

        
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      <a class="post-title-link" href="/2017/08/27/sort/">八大排序算法总结与java实现</a>
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        <blockquote>
<p>本文来自 Itimetraveler’s Blog： <a href="https://itimetraveler.github.io/2017/07/18/%E5%85%AB%E5%A4%A7%E6%8E%92%E5%BA%8F%E7%AE%97%E6%B3%95%E6%80%BB%E7%BB%93%E4%B8%8Ejava%E5%AE%9E%E7%8E%B0/" target="_blank" rel="noopener">八大排序算法总结与java实现</a></p>
</blockquote>
<h3 id="概述"><a href="#概述" class="headerlink" title="概述"></a>概述</h3><p>因为健忘，加上对各种排序算法理解不深刻，过段时间面对排序就蒙了。所以决定对我们常见的这几种排序算法进行统一总结，强行学习。首先罗列一下常见的十大排序算法：</p>
    

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	<ul class="article-tag-list"><li class="article-tag-list-item"><a class="article-tag-list-link" href="/tags/Java/">Java</a></li><li class="article-tag-list-item"><a class="article-tag-list-link" href="/tags/排序/">排序</a></li><li class="article-tag-list-item"><a class="article-tag-list-link" href="/tags/算法/">算法</a></li></ul>

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        <time class="post-time" title="2017-08-27 11:15:21" datetime="2017-08-27T03:15:21.000Z"  itemprop="datePublished">2017-08-27</time>

        
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    <h3 class="post-title" itemprop="name">
      <a class="post-title-link" href="/2017/08/27/hasmap2/">Java 8系列之重新认识HashMap</a>
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        <blockquote>
<p>本文来自美团点评技术团队： <a href="http://tech.meituan.com/java-hashmap.html" target="_blank" rel="noopener">Java 8系列之重新认识HashMap</a></p>
</blockquote>
<h2 id="摘要"><a href="#摘要" class="headerlink" title="摘要"></a><strong>摘要</strong></h2><p>HashMap是Java程序员使用频率最高的用于映射(键值对)处理的数据类型。随着JDK（Java Developmet Kit）版本的更新，JDK1.8对HashMap底层的实现进行了优化，例如引入红黑树的数据结构和扩容的优化等。本文结合JDK1.7和JDK1.8的区别，深入探讨HashMap的结构实现和功能原理。</p>
<h2 id="简介"><a href="#简介" class="headerlink" title="简介"></a><strong>简介</strong></h2><p>Java为数据结构中的映射定义了一个接口java.util.Map，此接口主要有四个常用的实现类，分别是<code>HashMap</code>、<code>Hashtable</code>、<code>LinkedHashMap</code>和<code>TreeMap</code>，类继承关系如下图所示：</p>
<p>[<figure class="image-bubble">
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                    <div class="overlay"></div>
                    <img src="http://img.blog.csdn.net/20170616165413193" alt="img](http://img.blog.csdn.net/20170616165413193)" title>
                </div>
                <div class="image-caption">img](http://img.blog.csdn.net/20170616165413193)</div>
            </figure></p>
    

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        <time class="post-time" title="2017-08-26 22:07:09" datetime="2017-08-26T14:07:09.000Z"  itemprop="datePublished">2017-08-26</time>

        
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    <h3 class="post-title" itemprop="name">
      <a class="post-title-link" href="/2017/08/26/myosi/">OSI七层模型</a>
    </h3>
  




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        <blockquote>
<p>开放系统互连参考模型 (Open System Interconnect 简称OSI）是国际标准化组织(ISO)和国际电报电话咨询委员会(CCITT)联合制定的开放系统互连参考模型，为开放式互连信息系统提供了一种功能结构的框架。它从低到高分别是：<a href="https://baike.baidu.com/item/%E7%89%A9%E7%90%86%E5%B1%82" target="_blank" rel="noopener">物理层</a>、<a href="https://baike.baidu.com/item/%E6%95%B0%E6%8D%AE%E9%93%BE%E8%B7%AF%E5%B1%82" target="_blank" rel="noopener">数据链路层</a>、<a href="https://baike.baidu.com/item/%E7%BD%91%E7%BB%9C%E5%B1%82" target="_blank" rel="noopener">网络层</a>、<a href="https://baike.baidu.com/item/%E4%BC%A0%E8%BE%93%E5%B1%82" target="_blank" rel="noopener">传输层</a>、会话层、<a href="https://baike.baidu.com/item/%E8%A1%A8%E7%A4%BA%E5%B1%82" target="_blank" rel="noopener">表示层</a>和<a href="https://baike.baidu.com/item/%E5%BA%94%E7%94%A8%E5%B1%82" target="_blank" rel="noopener">应用层</a>。</p>
</blockquote>
<p>下图为OSI七层模型图解:</p>
    

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        <time class="post-time" title="2017-08-26 19:50:16" datetime="2017-08-26T11:50:16.000Z"  itemprop="datePublished">2017-08-26</time>

        
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    <h3 class="post-title" itemprop="name">
      <a class="post-title-link" href="/2017/08/26/redis2/">Redis面试总结</a>
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        <blockquote>
<p><strong>本文转载至:<a href="http://www.cnblogs.com/jiahaoJAVA/p/6244278.html" target="_blank" rel="noopener">http://www.cnblogs.com/jiahaoJAVA/p/6244278.html</a></strong></p>
</blockquote>
<h2 id="（1）什么是redis"><a href="#（1）什么是redis" class="headerlink" title="（1）什么是redis?"></a>（1）什么是redis?</h2><p> <a href="http://lib.csdn.net/base/redis" target="_blank" rel="noopener">Redis</a> 是一个基于内存的高性能key-value<a href="http://lib.csdn.net/base/mysql" target="_blank" rel="noopener">数据库</a>。 (有空再补充，有理解错误或不足欢迎指正)</p>
<h2 id="（2）Reids的特点"><a href="#（2）Reids的特点" class="headerlink" title="（2）Reids的特点"></a>（2）Reids的特点</h2><p>Redis本质上是一个Key-Value类型的内存数据库，很像memcached，整个数据库统统加载在内存当中进行操作，定期通过异步操作把数据库数据flush到硬盘上进行保存。因为是纯内存操作，Redis的性能非常出色，每秒可以处理超过  10万次读写操作，是已知性能最快的Key-Value DB。</p>
    

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        <time class="post-time" title="2017-08-26 11:09:02" datetime="2017-08-26T03:09:02.000Z"  itemprop="datePublished">2017-08-26</time>

        
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    <h3 class="post-title" itemprop="name">
      <a class="post-title-link" href="/2017/08/26/sql-2/">SQL语句优化问题(续)</a>
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        <p>话不多说，接着上次的来。</p>
<p>（11）sql语句用大写的，因为oracle总是在解析sql语句时把小写的字母转换成大写的再执行。</p>
<p>（12）避免在索引列上使用NOT，NOT会产生在和在索引列上使用函数相同的影响。 当ORACLE”遇到”NOT,他就会停止使用索引转而执行全表扫描。</p>
<p>（13） 避免在索引列上使用计算，WHERE子句中，如果索引列是函数的一部分，优化器将不使用索引而使用全表扫描。</p>
<p>例如:</p>
<figure class="highlight sql"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line">低效：</span><br><span class="line"></span><br><span class="line"><span class="keyword">SELECT</span> …<span class="keyword">FROM</span>  DEPT  <span class="keyword">WHERE</span> SAL * <span class="number">12</span> &gt; <span class="number">25000</span>;</span><br><span class="line"></span><br><span class="line">高效:</span><br><span class="line"></span><br><span class="line"><span class="keyword">SELECT</span> …<span class="keyword">FROM</span> DEPT <span class="keyword">WHERE</span> SAL &gt; <span class="number">25000</span>/<span class="number">12</span>;</span><br></pre></td></tr></table></figure>
    

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      <a class="post-title-link" href="/2017/08/25/redis/">你的项目为甚么要使用Redis</a>
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        <blockquote>
<p><strong>本文摘自《Redis实战》</strong></p>
<p><strong>链接：<a href="http://www.epubit.com.cn/article/200" target="_blank" rel="noopener">http://www.epubit.com.cn/article/200</a></strong></p>
</blockquote>
<h2 id="Redis简介"><a href="#Redis简介" class="headerlink" title="Redis简介"></a>Redis简介</h2><p>Redis是一个远程内存数据库，它不仅性能强劲，而且还具有复制特性以及为解决问题而生的独一无二的数据模型。Redis提供了5种不同类型的数据结构，各式各样的问题都可以很自然地映射到这些数据结构上：Redis的数据结构致力于帮助用户解决问题，而不会像其他数据库那样，要求用户扭曲问题来适应数据库。除此之外，通过复制、持久化（persistence）和客户端分片（client-side sharding）等特性，用户可以很方便地将Redis扩展成一个能够包含数百GB数据、每秒处理上百万次请求的系统。</p>
    

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        <h2 id="一、图解SpringMVC"><a href="#一、图解SpringMVC" class="headerlink" title="一、图解SpringMVC"></a>一、图解SpringMVC</h2><h3 id="下面为SpringMVC的执行流程"><a href="#下面为SpringMVC的执行流程" class="headerlink" title="下面为SpringMVC的执行流程:"></a>下面为SpringMVC的执行流程:</h3><figure class="image-bubble">
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                <div class="image-caption">springmvc执行流程</div>
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        <p>​        系统优化中一个很重要的方面就是SQL语句的优 化。对于海量数据，劣质SQL语句和优质SQL语句之间的速度差别可以达到上百倍，可见对于一个系统不是简单地能实现其功能就可，而是要写出高质量的 SQL语句，提高系统的可用性。</p>
<p>​       在多数情况下，Oracle使用索引来更快地遍历表，优化器主要根据定义的索引来提高性能。但是，如果在SQL语句的where子句中写的 SQL代码不合理，就会造成优化器删去索引而使用全表扫描，一般就这种SQL语句就是所谓的劣质SQL语句。在编写SQL语句时我们应清楚优化器根据何种 原则来删除索引，这有助于写出高性能的SQL语句。</p>
<h2 id="一、造成索引失效的情况"><a href="#一、造成索引失效的情况" class="headerlink" title="一、造成索引失效的情况"></a>一、造成索引失效的情况</h2><h3 id="1-IS-NULL-与-IS-NOT-NULL"><a href="#1-IS-NULL-与-IS-NOT-NULL" class="headerlink" title="1.IS NULL 与 IS NOT NULL"></a>1.IS NULL 与 IS NOT NULL</h3>
    

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